Pumps

ABSTRACT

A pump assembly having a chamber into which a pump is arranged to discharge, and a plurality of outlet pipes each having one end extending into the chamber, the wall of each outlet pipe at said one end being of streamline form, and the part of each pipe extending away from said one end being in the form of a diffuser of gradually increasing internal cross-sectional area with increasing distance from the said one end.

ilnited States Patent [1 1 Lee [451 Sept. 24, 1974 1 PUMPS [75] Inventor: Alan Stuart Lee, Leicester, England [73] Assignee: The English Electric Company Limited, London, England [22] Filed: May 30, 1973 [21] Appl. No.2 365,163

[30] Foreign Application Priority Data May 31, 1972 Great Britain 25426/72 [52] US. Cl 415/207, 415/209, 415/216 [51] Int. Cl. F04d 29/44, F04d 29/54, F04d 15/02 [58] Field of Search 415/207, 210, 216, 501, 415/209, 217; 137/590; 417/424, 240, 241;

[56] References Cited UNITED STATES PATENTS 2,210,401 8/1940 Fulton 415/501 2,609,141 9/1952 Ave 415/210 2,694,296 11/1954 Prosek et a1. 138/44 3,333,762 8/1967 Urana 915/211 FOREIGN PATENTS OR APPLICATIONS 1,373,013 8/1964 France 415/219 OTHER PUBLICATIONS Byron Jackson Bulletin 37-5050, 1938 Primary Examiner-C. J. I-Iusar Assistant Examiner-Louis J. Casaregola Attorney, Agent, or Firm-Kirschstein, Kirschstein, Ottinger & Frank [57] ABSTRACT A pump assembly having a chamber into which a pump is arranged to discharge, and a plurality of outlet pipes each having one end extending into the chamber, the wall of each outlet pipe at said one end being of streamline form, and the part of each pipe extending away from said one end being in the form of a diffuser of gradually increasing internal cross-sectional area with increasing distance from the said one end.

5 Claims, 2 Drawing Figures PATENTEDSEPZMQM sum 2 OF 2 PUMPS This invention relates to pumps.

It is an object of the invention to provide a pump having an outlet arrangement which presents a smaller impedance to normal forward fluid flow from the pump than to flow in the reverse direction.

According to the present invention a pump assembly comprises a pump, achamber into which the pump is arranged to discharge, and at least one outlet pipe in communication at one of its ends with the interior of the chamber, the wall of the/or each outlet pipe at the said one of its ends being of streamline form and a part of the/or each pipe extending away from the said one end thereof being in the form of a diffuser of gradually increasing internal cross-sectional area with increasing distance from the said one end of the pipe.

In a preferred embodiment of the invention, the pump comprises a rotary centrifugal impeller and an annular axial diffuser having a first end arranged to receive pumped fluid from the impeller and a second end, of greater annular cross-sectional area than the first end, opening into the said chamber.

Conveniently the diffuser, whose second end opens into the chamber, itself constitutes a peripheral wall section of the chamber, into which its said second end opens peripherally, and the or each outlet pipe extends into the chamber, in the axial direction of the diffuser, with its said one end directed oppositely to and away from the said second end of the diffuser, whereby fluid flowing from the pump flows in one axial direction in the diffuser and in the or each outlet pipe but in the opposite direction whilst flowing, within the chamber, from the diffuser to the outlet pipe or pipes.

An embodiment of a pump assembly having an outlet arrangement according to the invention is described below, by way of illustrating the invention, with reference to the accompanying drawings, in which:

FIG. 1 is a view, partly in axial section, of the pump assembly, and

FIG. 2 is an axial sectional view, on a larger scale; of part of the pump assembly shown in FIG. 1.

The pump assembly shown in the drawings and indicated generally by the reference 11 is intended for use in circulating molten sodium as the reactor primary coolant in, for example, a civil fast reactor, and as shown in FIG. 1 is mounted vertically with its upper end secured in sealing engagement in an aperture 12 in a reactor containment vessel 13, with its lower end immersed below the surface level 14 of a reservoir of mo]- ten sodium 15 contained within the vessel 13. At its upper end the pump assembly 11 comprises an electric motor 16 for rotating a shaft 17 on the lower end of which is secured an impeller 18 provided with vanes 19. Rotation of the shaft 17 and impeller 18 impels molten sodium, in an annular duct 20 defined by fixed parts of the pump assembly and provided with fixed vanes 21 and 22, centrifugally outwards past the vanes 22. The duct 20 is below the surface level 14 of the sodium 15, and is thus kept filled with sodium which enters it past the vanes 21. The shaft 17 is supported near its lower end by a bearing 23 mounted by means of struts 24. The bearing 23 may, as shown, be a hydrostatic bearing and in that case it may, as shown, he supplied with molten sodium under pressure via a pipe 25 which bleeds off a small proportion of the sodium in the duct 20 in the vicinity of the vanes 22 and supplies it via one of the struts 24 to the bearing 23. This sodium then flows from the bearing into the space 26 surrounding the bearing and the shaft 17, this space being in any case filled with sodium up to the surface level 14 because it is open to the sodium 15 through apertures 27. The sodium impelled past the vanes 22 (apart from any bled to the bearing 23 as just described) then passes through an annular axial diffuser having coaxial outer end inner walls 28 and 29 and fixed vanes 30, the sodium entering this diffuser at a first, upper end thereof and being discharged therefrom at a second, lower, end thereof which is of greater annular cross-sectional area.

The pump assembly as described in the preceding paragraph-is of known kind, but in accordance with the present invention it is provided, as described below, with a chamber into which it discharges and with one or (as shown in the drawings) more outlet pipes in communication with the interior of the chamber.

The said chamber, indicated by the reference 31, is defined in part by the diffuser, which itself constitutes a peripheral wall section thereof, and is closed at its upper end by fixed parts of the pump assembly in the vicinity of the impeller 18 thereof. At its lower end the chamber 31 is closed by a dished or bowl-shaped plate 32 which is secured in sealed manner, for example by welding, to the lower end of the outer wall 28 of the diffuser. The plate 32 is apertured to receive, in sealed engagement therewith, four outlet pipes 33 which extend in the axial direction and project upwardly into the chamber 31 with an end 34 of each pipe in communication with the interior of the chamber. The wall of each outlet pipe, at its end 34, is of streamline form so that as sodium flows into the pipes 33 from the chamber 31 there is little or no separation of the fluid flow from the pipe walls. A part 35 of each pipe 33, extending away from the end 34 thereof, is in the form of a diffuser, being of gradually increasing internal cross-sectional area with increasing distance from the end 34, whereby little or no turbulence is introduced into the sodium as it flows from the end 34 of a pipe 33 to the greaterdiameter part thereof below the part 33.

As already described, the illustrated pump assembly is shown mounted in a nuclear reactor; and the outlet pipes 33 would convey the pumped liquid sodium from the pump assembly to a core of the reactor, where it would be distributed to nuclear fuel elements within the core. Fourpipes 33 are associated with the pump assembly as a safety factor, so that in the event of a failure of one of the pipes a reduced but still sufficient, proportion of the output of the pump assembly will continue to reach the fuel elements. It will be understood that in other applications in which such safety considerations do not apply a pump assembly in accordance with the invention might be provided with less outlet pipes and perhaps with only one.

A further consideration when (as would be the case in a nuclear reactor) a plurality of pumps are operating in parallel in a fluid-flow system is that it will usually be desirable or essential that even a complete failure of one of the pumps should not result in the system as a whole being subjected to a leakage so serious as to prevent the remaining pumps from maintaining a reduced but still satisfactory supply to the intended destination of the pumped fluid; and the pump outlet means according to the invention enables this desirable object to be achieved, as will not be explained. In normal operation of the illustrated pump assembly, the sodium impelled by the impeller 18 enters the diffuser at relatively high speed and, as it passes from the upper end of the diffuser to the lower end thereof which is of greater annular cross-sectional area, its speed is reduced and part of its kinetic energy is converted, almost without loss, into pressure energy. Sodium in the chamber 31, under the relatively high pressure which thus obtains there, flows into the ends 34 of the outlet pipes 33 and, because of the relatively small total internal cross-sectional area of the pipes 33 at their ends 34, as compared with that of the chamber 31 in which the sodium flows to those ends, the flow rate of the sodium in the ends 34 of the pipes is relatively high. The streamline form of the pipe walls at their ends 34 ensures, however, that the flow is substantially nonturbulent and that the conversion of pressure energy to kinetic energy is effected with little loss of energy. The provision of the pipe sections 35 in the form of diffusers then provides a smooth transition, again with negligible energy loss, from the ends 34 to the main runs of the pipes 33 which are of wider bore and in which, accordingly the kinetic energy of the flowing sodium is less again-In the event of failure of one of several pumps 11 acting in parallel, however (or, equally, in the event that the chamber 31 associated with one of several such pumps becomes fractured so that the output from the pump is lost by leakage), the flow of sodium in the pipes 33 associated with that pump and that chamber 31 will be reversed due to the pressure from the outputs of the other pumps; and it is important for safety reasons that this reverse flow should be minimised so as not to constitute a serious leakage of the outputs from the other pumps. Satisfactory minimisation of such reverse flow is, in fact, achieved by the arrangement described above, because the diffuser sections 35 and ends 34 of the pipes 33, opening into the chamber 31, present a much greater impedance to flow in the reverse direction than to flow in the forward direction. This is because, for flow in the reverse direction, the ends 34 of the pipes 33 open abruptly into the much greater cross-sectional area of the chamber 31 and the reverse flow becomes turbulent with large dissipation of energy. Thus high flow rates in the reverse direction are prevented, and the possible diversion, due to leakage, of the outputs from the other pumps, is limited. The described configuration acts, in fact, as a fluid diode.

The provision of the chamber 31 between the pump and the pipes 33 also confers another benefit, of a different kind. It is well known that acoustic waves are transmitted with little attenuation along a fluid in a pipe of constant or only slightly varying cross section, and this could lead, in a reactor coolant system, to noise (including high frequency noise) generated in a pump of the system producting, in other parts of the reactor, vibrations which could be dangerous or could interfere with instrumentation of the reactor. For example, one method of detecting failed fuel elements in a reactor is by means of hydrophones, in the fuel channels, which detect the noise from boiling of the sodium coolant in the vicinity of a ruptured fuel element container. Such boiling is known to produce noise most effectively at high frequencies of the order of 100 KHZ, and noise of similar frequencies may also be produced by cavitation of a pump. It is therefore important that such high frequency noise, generated in the pump unit 11, should be attenuated before it reaches the fuel channels to which it would otherwise be transmitted by the pipes 33. In the illustrated configuration the chamber 31, with its greater cross-section than that of the diffuser constituted by the walls 28 and 29, and then that of the pipe ends 34, and the fact that the pipe ends 34 are directed away from the end of the diffuser opening into the chamber 31, mean that accoustic waves in the sodium can only be transmitted to the pipes 33 after multiple reflection at which attenuation occurs. Also the restricted cross-sections of the pipe ends 33 severely limit the entry of sodium-transmitted acoustic waves into the sodium in the pipes 33. Thus an attenuation of sodiumtransmitted noise, including high frequency noise, takes place between the pump and the pipes 33.

I claim:

1. A pump assembly comprising:

a. a pump;

b. a chamber into which the pump is arranged to discharge;

c. at least one outlet pipe in communication at one of its ends with the interior of the chamber;

d. a wall defining each outlet pipe at said one of its ends being of streamline form;

a part of each outlet pipe extending away from the said one end thereof being in the form of a diffuser of gradually increasing internal cross-sectional area with increasing distance from the said one end of the outlet pipe;

f. the total internal cross-sectional area of the said one end of the outlet pipes being small compared with the internal cross-sectional area of the chamher; and

g. the said one end of each outlet pipe opening abruptly into the much greater cross-sectional area of the chamber so that the arrangement of outlet pipes and chamber acts as a fluid diode.

2. A pump assembly as claimed in claim 1, wherein the pump comprises a rotary centrifugal impeller, and there is provided a further annular axial diffuser having a first end arranged to receive pumped fluid from the impeller and a second end, of greater annular crosssectional area than the first end, opening into the said chamber.

3. A pump assembly as claimed in claim 2 wherein the second end of said annular axial diffuser constitutes a peripheral wall section of said chamber into which its second end opens peripherally, and each outlet pipe extends into the chamber in the axial direction of the said annular axial diffuser with its said one end directed oppositely to and away from the second end of the annular axial diffuser, whereby fluid flowing from the impeller flows in one axial direction through the annular axial diffuser and through each difiuser formed by a part of an outlet pipe, but flows in the opposite axial direction while flowing, within said chamber, from said annular axial diffuser to each diffuser formed by a part of an outlet pipe.

4. A pump assembly as claimed in claim 3 wherein the pump is located above the chamber and each outlet pipe extends downwards from the chamber with the said one end extending upwards into the chamber.

5. A pump assembly as claimed in claim 4 having four outlet pipes in communication with the interior of the chamber. 

1. A pump assembly comprising: a. a pump; b. a chamber into which the pump is arranged to discharge; c. at least one outlet pipe in communication at one of its ends with the interior of the chamber; d. a wall defining each outlet pipe at said one of its ends being of streamline form; e. a part of each outlet pipe extending away from the said one end thereof being in the form of a diffuser of gradually increasing internal cross-sectional area with increasing distance from the said one end of the outlet pipe; f. the total internal cross-sectional area of the said one end of the outlet pipes being small compared with the internal cross-sectional area of the chamber; and g. the said one end of each outlet pipe opening abruptly into the much greater cross-sectional area of the chamber so that the arrangement of outlet pipes and chamber acts as a fluid diode.
 2. A pump assembly as claimed in claim 1, wherein the pump comprises a rotary centrifugal impeller, and there is provided a further annular axial diffuser having a first end arranged to receive pumped fluid from the impeller and a second end, of greater annular cross-sectional area than the first end, opening into the said chamber.
 3. A pump assembly as claimed in claim 2 wherein the second end of said annular axial diffuser constitutes a peripheral wall section of said chamber into which its second end opens peripherally, and each outlet pipe extends into the chamber in the axial direction of the said annular axial diffuser with its said one end directed oppositely to and away from the second end of the annular axial diffuser, whereby fluid flowing from the impeller flows in one axial direction through the annular axial diffuser and through each diffuser formed by a part of an outlet pipe, but flows in the opposite axial direction while flowing, within said chamber, from said annular axial diffuser to each diffuser formed by a part of an outlet pipe.
 4. A pump assembly as claimed in claim 3 wherein the pump is located above the chamber and each outlet pipe extends downwards from the chamber with the said one end extending upwards into the chamber.
 5. A pump assembly as claimed in claim 4 having four outlet pipes in communication with the interior of the chamber. 